Method for manufacturing an injection molded body

Abstract

The object of the present invention is to provide a method for manufacturing injection-molded articles of resin compositions containing P3HA-type resins that can be stably and continuously produced without burrs. The present invention solves the above-mentioned problem by providing a method for manufacturing injection-molded articles using a mold apparatus employing a resin composition containing P3HA-type resins, wherein the P3HA-type resin is a copolymer comprising at least one copolymer of 3HB units and other hydroxyalkyl ester units, the maximum width of the parting line connecting to the cavity within the mold in the mold apparatus is 30 μm or less, and a venting portion is provided at a specific location within the mold, the maximum width of the opening of the venting portion being 1 to 50 μm.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an injection-molded article using a mold device containing a resin composition of a poly(3-hydroxyalkanoate) resin (hereinafter sometimes referred to as "P3HA resin"). Background Technology

[0002] In recent years, environmental problems caused by waste plastics have attracted attention, especially the large quantities of plastics that are known to drift in the oceans globally through dumping and rivers. Because such plastics retain their shape for a long time, they have been pointed out to have impacts on ecosystems such as trapping marine life (so-called ghost fishing) and remaining in the digestive organs of marine organisms, causing feeding difficulties.

[0003] In addition, microplastics, which are formed by the degradation / micronization of plastics due to ultraviolet rays and other factors, can adsorb harmful compounds in the ocean. It has also been pointed out that these microplastics can enter the food chain through ingestion by marine organisms.

[0004] Regarding the marine pollution caused by plastics, the use of biodegradable plastics is expected. However, a 2015 report compiled by the United Nations Environment Programme pointed out that plastics such as polylactic acid, which can be biodegraded with mixed fertilizers, cannot be expected to degrade in the low-temperature ocean in a short period of time, and therefore cannot be used as a solution to marine pollution.

[0005] Among them, P3HA resins are biodegradable materials that can also be used in seawater, and therefore have attracted much attention as raw materials for solving the above problems.

[0006] For example, Patent Document 1 discloses a method for manufacturing an injection molded article, which is a method for manufacturing an injection molded article from a molding material containing a poly(3-hydroxybutyrate) resin. The method includes: heating and melting the molding material such that the difference between the melting point peak temperature and the melting point peak end temperature in differential scanning calorimetry is 10°C or more and 70°C or less, and injecting the molding material into a mold with a temperature in the range of 30 to 80°C; and cooling the molding material in the mold to crystallize and solidify it.

[0007] In addition, Patent Document 2 discloses a mold apparatus for injection molding of a biodegradable resin comprising poly(3-hydroxyalkanoate). The mold apparatus includes: a hot runner for heating and melting the biodegradable resin; a plurality of cavities for injecting and filling the molten resin heated and melted in the hot runner; and an ingate connecting the hot runner and the cavities. The flow length of the biodegradable resin from the position of the ingate to the final filling position in the cavity is the same in the plurality of cavities.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: International Publication No. 2021 / 010054

[0011] Patent Document 2: Japanese Patent Application Publication No. 2021-020431 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] Although the above technologies are excellent, even combining them cannot fully meet the requirements for reducing burrs, and can be considered insufficient for stable production.

[0014] Therefore, the object of the present invention is to provide a method for manufacturing injection molded articles of resin compositions containing P3HA-type resins that can be stably and continuously produced without burrs.

[0015] Methods for solving problems

[0016] In order to solve the above-mentioned problems, the inventors conducted in-depth research and discovered for the first time that in the manufacture of injection-molded articles of P3HA resins containing copolymers of at least one 3-hydroxybutyrate (hereinafter also referred to as "3HB") unit and other hydroxyalkanoate units, especially P3HA resins with a low ratio of 3-hydroxyhexanoate (hereinafter also referred to as "3HH") units (i.e., P3HA resins with a high ratio of 3HB units), by using a specific mold, it is possible to achieve stable continuous production without burrs, thereby completing the present invention.

[0017] Therefore, one aspect of the present invention is a method for manufacturing an injection-molded article, which uses a mold device containing a resin composition of a P3HA type resin, wherein the P3HA type resin is a copolymer containing at least one of the following copolymers: a copolymer of 3HB unit and other hydroxyalkanoate units, wherein when the mold in the mold device is closed, the maximum width of the parting line in contact with the cavity in the mold is 30 μm or less, and an vent is provided at a location different from the parting line in contact with the cavity in the mold, wherein the maximum width of the opening of the vent is 1 to 50 μm.

[0018] The effects of the invention

[0019] According to one aspect of the present invention, in the manufacture of injection-molded articles of resin compositions containing P3HA-type resins, burr-free and stable continuous production is possible. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating a general outline of a mold apparatus according to one embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram showing the state of the mold when it is opened according to one embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram showing the closed state of a mold according to one embodiment of the present invention.

[0023] Figure 4 This is a schematic diagram showing the closed state of a mold with an venting section having an opening in the form of a slit, according to an embodiment of the present invention.

[0024] Figure 5 This is a schematic diagram showing the closed state of a mold with an opening and a sleeve-type venting section according to an embodiment of the present invention.

[0025] Symbol Explanation

[0026] 1 mold (convex part)

[0027] 2 mold (concave part)

[0028] 3. Mold

[0029] 10 Mold Device

[0030] 11 DC Channel

[0031] 12 Crossflow Channel

[0032] 13 Inner gate

[0033] 14 Nozzles

[0034] 21 Parting line that connects to the cavity inside the mold

[0035] 31-type cavity

[0036] 41 Exhaust section

[0037] 42 Slits

[0038] 43 Sleeve

[0039] 44. Exhaust section opening (sleeve type)

[0040] 51 Top pin

[0041] 61 Injection Molding Machine Detailed Implementation

[0042] The following describes one embodiment of the present invention in detail. It should be noted that, unless otherwise specified, in this specification, "A to B" indicating a numerical range means "A or more, and B or less". Furthermore, all documents described in this specification are incorporated herein by reference.

[0043] [1. Summary of the Invention]

[0044] A method for manufacturing an injection-molded article using a mold device containing a resin composition of P3HA type resin according to an embodiment of the present invention (hereinafter referred to as "the manufacturing method") is characterized in that the P3HA type resin is a copolymer containing at least one of the following copolymers: a copolymer of 3HB unit and other hydroxyalkanoate units; when the mold in the mold device is closed, the maximum width of the parting line in contact with the cavity in the mold is 30 μm or less; and an venting portion is provided at a location different from the parting line in contact with the cavity in the mold, the maximum width of the opening of the venting portion being 1 to 50 μm.

[0045] As mentioned above, P3HA resins are biodegradable even in seawater, making them a promising raw material for addressing marine pollution caused by the aforementioned plastics. However, P3HA resins have a slow curing speed, making them difficult to process, especially in injection molding where achieving a balance between burrs and shrinkage marks is challenging.

[0046] In their research on the manufacture of injection-molded articles using P3HA resins, the inventors discovered that, compared to other resins, P3HA resins containing copolymers of at least one 3HB unit and other hydroxyalkanoate units, especially P3HA resins with a low ratio of 3HH units (P3HA resins with a high ratio of 3HB units), are prone to burr formation.

[0047] Therefore, the inventors conducted in-depth research to solve the above-mentioned problems and found that by setting the maximum width (maximum clearance) of the parting line of the mold to a given value or less, the generation of burrs can be suppressed. On the other hand, when the maximum width of the parting line is set to a given value or less, a new problem of difficulty in venting arises. Therefore, the inventors further provided venting sections at locations different from the parting line of the mold, enabling stable and continuous production without the generation of burrs.

[0048] In previous technologies, the manufacture of injection-molded articles from P3HA-based resins mainly focused on conditions such as the melting point peak temperature or flow length of the resin used as a raw material. In contrast, the inventors discovered the aforementioned new challenges during the manufacture of injection-molded articles from P3HA-based resins, and in particular, by focusing on the mold structure, successfully manufactured injection-molded articles with fewer burrs.

[0049] According to the invention of this application, stable and continuous production is possible without the generation of burrs, making it extremely useful in the manufacture of injection-molded articles using P3HA resins (especially P3HA resins with a high 3HB ratio). The manufacturing method of this invention will now be described in detail.

[0050] [2. Manufacturing method of injection molded articles]

[0051] This manufacturing method is a method for manufacturing injection-molded articles using a mold device that utilizes a resin composition containing a P3HA-type resin. The P3HA-type resin is a copolymer comprising at least one of the following copolymers: a copolymer of 3HB units and other hydroxyalkyl ester units. Furthermore, in this manufacturing method, when the mold in the mold device is closed, the maximum width of the parting line connecting to the cavity within the mold is 30 μm or less, and an venting portion is provided at a location different from the parting line connecting to the cavity within the mold, with the maximum width of the opening of the venting portion being 1 to 50 μm.

[0052] In this specification, "parting line that connects to the cavity within the mold" refers to the gap between the mold surfaces that occurs when the mold is closed. That is, "parting line that connects to the cavity within the mold" refers to a gap that does not exist when the mold is open, but only exists when the mold is closed. In this specification, "parting line that connects to the cavity within the mold" is sometimes simply referred to as "parting line".

[0053] (Mold assembly)

[0054] use Figure 1 One embodiment of the mold apparatus (hereinafter also referred to as "this mold apparatus") used in this manufacturing method will be described in detail. It should be noted that... Figure 1 The mold apparatus described herein is only one example, and the mold apparatus used in this manufacturing method is not limited to that described herein. Figure 1 .

[0055] Figure 1 This is a schematic top view illustrating the outline of the mold assembly. (As shown) Figure 1 As shown, the mold assembly 10 consists of an injection molding machine 61 and a mold 3. In addition, the mold 3 has a straight runner 11, a cross runner 12, an ingate 13, and one or more cavities 31.

[0056] The resin composition, serving as the raw material for the injection molded article, is injected in a flowing (molten) state from the nozzle 14 of the injection molding machine 61 and fills the runner 11 within the mold 3. Then, the flowing resin composition passes from the runner 11 through the cross runner 12 and through the ingate 13 into the cavity 31. After the resin composition filled into the cavity 31 solidifies, it is cut off in the ingate 13, thereby obtaining the injection molded article from the mold 3.

[0057] The straight runner 11 is the portion that conveys the aforementioned resin composition to the cross runner 12. The cross runner 12 connects the straight runner 11 to the ingate 13. The cross runner 12 can branch, in which case the straight runner 11 can be connected to multiple ingates 13. The cross runner 12 can be a hot cross runner or a cold cross runner. The ingate 13 is an opening connecting the cross runner 12 to the cavity 31.

[0058] Next, use Figure 2 and 3 A detailed description of mold 3 in this mold assembly 10 is provided. It should be noted that... Figure 2 and 3 The mold described herein is only one example, and the molds used in this manufacturing method are not limited to those described herein. Figure 2 and 3 .

[0059] Figure 2 This is a schematic cross-sectional view showing the mold 3 in its open state. Additionally, Figure 3 This is a schematic top view and cross-sectional view showing the mold 3 in its closed state. The mold portion of the mold 3 is composed of a mold (protrusion) 1 and a mold (recess) 2. The mold (protrusion) 1 has a straight runner 11, a cross runner 12, and an ingate 13. In addition, the mold (recess) 2 has a cavity 31 for the resin composition to flow into. When the mold (protrusion) 1 and the mold (recess) 2 are combined (when closed), a parting line 21 is generated at the interface between the molds.

[0060] The maximum width (maximum gap) of the parting line 21 of the mold 3 (hereinafter also referred to as "this mold") constituting the mold apparatus 10 is 30 μm or less, preferably 20 μm or less, more preferably 10 μm or less, and even more preferably substantially no gap (i.e., 0 μm). As is commonly used in the prior art, when the maximum width of the parting line 21 is greater than 30 μm, in the case of using a P3HA type resin with a high ratio of 3HB units in this manufacturing method, the molten resin composition tends to leak to the outside of the cavity 31. Therefore, by making the maximum width of the parting line 21 30 μm or less, the resin composition is less likely to leak to the outside of the cavity 31, and the burrs of the resulting molded article are reduced.

[0061] The shape of the cavity 31 is not particularly limited, but a shape suitable for multiple molding processes is preferred. Examples of injection molded bodies formed in the cavity 31 that are disposable after use include: spoons, forks, knives, stirring rods, coffee capsules, trays, cups, wide-mouth bottles, straps, bottle caps, pen caps, pens, agricultural clips, and the frame of a fan. Preferably, the injection molded body is a disposable food-grade molded body, and examples include: spoons, forks, knives, stirring rods, coffee capsules, trays, and cups. Furthermore, the injection molded product is more preferably tableware. Examples of such tableware include: spoons (e.g., using...) Figures 1-4 The cavity 31 shown depicts spoons, forks, knives, stirring rods, etc. The above-described injection-molded bodies are preferably used in agriculture, fisheries, forestry, horticulture, medicine, hygiene products, clothing, non-clothing products, packaging, and other fields.

[0062] like Figure 1 As shown, the mold 3 preferably has two or more cavities 31 of the same shape, more preferably four or more, even more preferably eight or more, and particularly preferably sixteen or more.

[0063] By having the mold assembly 10 have multiple cavities 31 of the same shape, it is possible to manufacture injection molded parts of the same quality in large quantities and simultaneously. Therefore, stable and continuous production of injection molded parts can be carried out more efficiently.

[0064] For this mold assembly 10, it is preferable that the distance from the front end of the nozzle 14 of the injection molding machine 61 to each of the aforementioned cavities 31 is equal. Specifically, for example, it is preferable that... Figure 1 The shape shown. In Figure 1 In the case of the shape shown, the distance from the front end of the nozzle 14 of the injection molding machine 61 to each cavity 31 can be considered equal. It should be noted that... Figure 1 The injection molding apparatus shown is an example, and the shape of the injection molding apparatus used in this manufacturing method is not limited to this. For example, the shape of the cross runner 12 of this mold 3, in addition to... Figure 1 In addition to the shape shown, it can also be a shape with further depth (a three-dimensional shape). In the case that the cross runner 12 is a shape with depth, from the viewpoint of making the above-mentioned distances equal, it is preferable that the shape of the cross runner 12 has a linearly symmetrical shape with the injection molding machine 61 as the center (i.e., has multiple identical shapes).

[0065] When the mold device 10 is configured as described above, the distance from the nozzle 14 to the cavity 31 is the same, thereby enabling the resin to be filled into each cavity at substantially the same time, which helps to improve productivity.

[0066] In this mold 3, the resin composition within the direct flow channel 11 and the cross flow channel 12 is preferably in a molten (flowing) state. That is, the direct flow channel 11 and the cross flow channel 12 are preferably heated to above the melting point of the resin composition by means of a heater, infrared radiation, or the like. In other words, it is preferable that the resin composition is supplied to the cavity 31 from the cross flow channel 12 in a molten state. Therefore, the cross flow channel 12 in this manufacturing method is preferably a heated cross flow channel.

[0067] When the resin composition in the direct flow channel 11 and the cross flow channel 12 is in a molten state, it can supply resin to the entire cavity 31 in a balanced manner, thus reducing the likelihood of burrs forming in the injection molded body. In addition, there is virtually no waste material of the resin composition used as raw material.

[0068] The ingate 13 of this mold 3 is preferably operable. The mechanism for opening and closing the ingate 13 is not particularly limited; for example, it can be opened and closed using a valve pin (not shown) provided within the runner 12. When the runner 12 is equipped with a valve pin, the valve pin is positioned within the flow path of the resin composition in the runner 12. Furthermore, the outer diameter of the front end of the valve pin on the mold side is preferably formed to be substantially the same as, or slightly smaller than, the inner diameter of the ingate 13.

[0069] When the ingate 4 is closed at the aforementioned front end of the valve pin, the resin composition will not be discharged from the ingate 13. Furthermore, the injection molding apparatus preferably includes a mechanism for reciprocating the valve pin. In this case, the valve pin is configured to reciprocate up and down within the flow path of the resin composition in the cross runner 12 via this mechanism; therefore, the ingate 13 can be opened and closed by the up-and-down reciprocating motion of the valve pin.

[0070] Therefore, if the ingate 13 can be switched using a valve pin or similar switching mechanism, the resin composition can be effectively disconnected from the ingate 13 when the discharge of the resin composition from the ingate 13 is stopped. Thus, the discharge rate of the resin composition from the runner 12 can be more precisely controlled.

[0071] In this mold 3, the total volume of the straight runner 11, the cross runner 12 and the inner gate 13 / the total volume of the cavity 31 is preferably 0.5 to 5.0, more preferably 0.8 to 4.0, further preferably 1.0 to 3.0, and particularly preferably 1.0 to 2.0.

[0072] With the above configuration, the residence time of the resin composition in the direct flow channel 11 and the cross flow channel 12 is shortened. When the residence time of the resin composition is short, the temperature is more likely to become uniform, and thermal decomposition of the resin composition is less likely, thus resulting in an injection-molded body with fewer burrs. It should be noted that the "total volume of the cavity" can also be referred to as the "total volume of the product."

[0073] This mold 3 has an venting section 41 at a location different from the parting line 21. Use Figure 4 The exhaust section 41 is described in detail. Figure 4 This is a schematic top view and cross-sectional view of the mold showing the vent 41 in its closed state. The location of the vent 41 is not limited to... Figure 4 The part shown can be any part that is different from the parting line 21. In addition, there is no particular limitation on the number of exhaust parts 41, for example, 1, 2, 3, 4, or more than 5.

[0074] When the aforementioned resin composition is filled into the cavity 31, the air present in the cavity and the trace amounts of gas generated by the molten resin are compressed and placed under high pressure, making it difficult to fill the cavity 31 with the resin composition. Therefore, it is necessary to expel the gas. In the prior art, the gas is expelled from the parting line 21, etc. However, as described above, the maximum width of the parting line 21 of this mold is very narrow, making it impossible to fully expel the gas. Therefore, for this mold, the gas in the cavity 31 can be expelled to the outside by providing an venting section 41 at a location different from the parting line 21.

[0075] The mold 3 preferably has a mechanism for drawing gas from the exhaust section 41. The mechanism for drawing gas is not particularly limited, and examples include, for instance, a water-sealed vacuum pump and a dry Roots-type vacuum pump. However, from the viewpoint of excellent suction capacity, a vacuum pump is preferred.

[0076] By equipping the venting section 41 with a gas suction mechanism, the gas inside the cavity 31 can be discharged more efficiently, thus improving the productivity of the injection molded article.

[0077] The maximum width of the opening of the venting section 41 is 1 to 50 μm, preferably 2 to 40 μm, more preferably 3 to 30 μm, and even more preferably 3 to 15 μm. When the maximum width of the opening of the venting section 41 is 50 μm or less, it can effectively discharge gas and reduce burrs. In addition, when the width of the venting section is 1 μm or more, it can effectively discharge gas from the cavity 31.

[0078] Furthermore, the structure of the opening of the exhaust section 41 is preferably selected from one or more of the following: slit type, multi-hole type, sleeve type, and switch type. When the structure of the opening of the exhaust section 41 is as described above, the gas inside the cavity 31 can be easily discharged.

[0079] The slit method refers to forming a slit 42 of 1–50 μm on the surface of the cavity 31, and allowing gas to escape from the cavity 31 through the slit 42. The structure of the slit method is, for example, as shown below. Figure 4This indicates that, in the case where the opening of the exhaust section 41 is a slit, for example, as... Figure 4 As shown, the venting section 41 includes a slit 42. In the structure of the opening of the venting section 41, a porous method refers to a method where the pores in the porous material are connected to each other, ultimately venting the gas outside the cavity 31. A sleeve method refers to a method where a portion of the cavity 31 is used as a sleeve, venting the gas outside the cavity through the production gap. The sleeve method structure is, for example, as shown below. Figure 5 This indicates that, in the case where the opening of the exhaust section 41 is a sleeve, for example, as... Figure 5 As shown, the venting section 41 includes a sleeve 43. Gas inside the cavity 31 is discharged through the opening (sleeve type) 44 of the venting section, which connects the sleeve 43 to the cavity 31. The "switching type" refers to a condition where the venting section is open from the stage when molten resin is filled into the cavity 31 until it reaches the switching section, and closed when gas is discharged outside the cavity 31 and just before the molten resin reaches the switching section. In any configuration of the venting section 41, the maximum width of the opening is preferably 1 to 50 μm.

[0080] When multiple exhaust sections 41 exist, the maximum width of the opening of each exhaust section 41 may be the same or different. In addition, multiple types of opening structures of the exhaust sections 41 may be combined.

[0081] The mold 3 may further include a mechanism for removing the injection-molded part from the cavity 31. Examples of such a mechanism include... Figure 4 The ejector pin 51 is shown. When this mold 3 is equipped with the above-mentioned mechanism, the venting part 41 can be set at the same position as the ejector pin 51.

[0082] (P3HA type resin)

[0083] The resin composition used in this manufacturing method comprises a P3HA resin. In this specification, "P3HA resin" refers to a biodegradable aliphatic polyester (preferably a polyester without aromatic rings). A P3HA resin is a 3-hydroxyalkanoate repeating unit represented by the general formula: [-CHR-CH2-CO-O-] (where R is a carbonyl ester repeating unit). n H 2n+1 Polyhydroxyalkanoates (where n is an integer greater than or equal to 1 and less than or equal to 15) are repeated units of alkyl groups.

[0084] Furthermore, the aforementioned P3HA resin is a copolymer containing at least one of the following copolymers: a copolymer of 3HB units and other hydroxyalkanoate units. The 3-hydroxybutyrate units in the aforementioned poly(3-hydroxyalkanoate) resin are preferably 80.0–99.5 mol% of all repeating units (100 mol%), more preferably 90.0–99.0 mol%, further preferably 93.0–98.7 mol%, and even more preferably 94.0–98.5 mol%.

[0085] By making the composition ratio of 3HB repeating units 80.0 mol% or more, the rigidity of P3HA resins is further improved, and there is a tendency to increase productivity by accelerating crystallization and reducing burrs. On the other hand, by making the composition ratio of 3HB repeating units 99.5 mol% or less, the melting point is lower than the thermal decomposition temperature, thus enabling stable and continuous production. It should be noted that the monomer composition ratio of P3HA resins can be determined by methods such as gas chromatography (for example, refer to International Publication No. 2014 / 020838).

[0086] More specifically, P3HA resins are copolymers of 3HB and other hydroxyalkyl esters, such as: poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-copoly-3-hydroxyvalerate) (P3HB3HV), poly(3-hydroxybutyrate-copoly-3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate-copoly-3-hydroxyvalerate-copoly-3-hydroxyhexanoate) (P3HB3HV3HH), poly(3-hydroxybutyrate-copoly-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-copoly-3-hydroxyoctanoate), poly(3-hydroxybutyrate-copoly-3-hydroxydecanoate), etc.

[0087] It should be noted that microbially produced P3HA resins (microbially generated P3HA resins) are typically P3HA resins composed solely of polyhydroxyalkanoate monomer units in the D-body (R-body) form. From the viewpoint of ease of industrial production, P3HB, P3HB3HH, P3HB3HV, P3HB3HV3HH, and P3HB4HB are preferred among microbially generated P3HA resins, and more preferably P3HB, P3HB3HH, P3HB3HV, and P3HB4HB.

[0088] Microorganisms that produce P3HA-type resins are not limited to any specific type of microorganism capable of producing P3HA-type resins. For example, the earliest P3HB-producing bacterium discovered in 1925 is *Bacillus megaterium*. Other examples include: *Cupriavidus necator* (formerly classified as *Alcaligenes eutrophus* and *Ralstonia eutropha*), and *Alcaligenes latus*, among other naturally occurring microorganisms. In these microorganisms, P3HB is known to accumulate within the bacterial cell.

[0089] In addition, as a producer of copolymers of hydroxybutyrate and other hydroxyalkyl esters, *Aeromonas caviae* is known as a producer of P3HB3HV and P3HB3HH, and *Alcaligenes eutrophus* is known as a producer of P3HB4HB. Especially regarding P3HB3HH, to improve the productivity of P3HB3HH, *Alcaligenes eutrophus* strain AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, p4821-4830 (1997)) which has been introduced with genes from the P3HA resin synthase group, is more preferred. By culturing these microorganisms under appropriate conditions, microbial cells that allow P3HB3HH to accumulate within the cells can be used. In addition to the above, recombinant microorganisms with various P3HA resin synthesis-related genes can also be used depending on the desired P3HA resin production, as long as the culture conditions, including the type of substrate, are optimized.

[0090] The molecular weight of P3HA resins is not particularly limited, as long as it exhibits substantially sufficient physical properties for the intended application. The weight-average molecular weight range of P3HA resins is preferably 100,000 to 1,000,000, more preferably 150,000 to 700,000, further preferably 200,000 to 500,000, and particularly preferably 250,000 to 450,000. When the weight-average molecular weight is 100,000 or higher, moderate mechanical strength can be obtained. Furthermore, when the molecular weight is below 1,000,000, the increase in melt viscosity can be suppressed, resulting in excellent moldability.

[0091] The above-mentioned method for determining the weight-average molecular weight can be performed using a gel permeation chromatography (GPC) system (Shodex GPC-101, manufactured by Showa Denko Corporation), using a polystyrene gel column (Shodex K-804, manufactured by Showa Denko Corporation), with chloroform as the mobile phase, and calculating the molecular weight in the form of polystyrene after conversion. Calibration curves were then constructed using polystyrene with weight-average molecular weights of 31,400, 197,000, 668,000, and 1,920,000. Suitable columns for determining these molecular weights can be used as the columns for this GPC system.

[0092] In addition to the aforementioned P3HA resin, the resin composition in this manufacturing method may also contain a second P3HA resin. The second P3HA resin comprises a copolymer of at least one 3HB unit and other hydroxyalkyl ester units. The 3HB unit in the poly(3-hydroxyalkyl ester) resin is preferably 65.0 to 90.0 mol, more preferably 68.0 to 88.0 mol, and even more preferably 70.0 to 85.0 mol. By further including the second P3HA resin in the above resin composition, the molded article exhibits excellent toughness.

[0093] The second P3HA type resin may differ from the P3HA type resin described above, and there is no particular limitation. Examples of the resins exemplified as the second P3HA type resin include those described above.

[0094] The content of the second P3HA resin is not particularly limited, but is preferably 50 parts by weight or less, more preferably 45 parts by weight or less, and even more preferably 40 parts by weight or less, relative to 100 parts by weight of all P3HA resin. The lower limit of the content of the second P3HA resin is not particularly limited and can be 0 parts by weight. It should be noted that the aforementioned P3HA resin can be used as the second P3HA resin. Furthermore, in this specification, "all P3HA resin" refers to all P3HA resin contained in the resin composition of this manufacturing method.

[0095] Without impairing the effects of the present invention, the above-described resin composition may contain resins other than P3HA resins. Examples of such other resins include aliphatic polyester resins such as polybutylene adipate, polybutylene succinate, polycaprolactone, and polylactic acid; aliphatic aromatic polyester resins such as polybutylene adipate, polybutylene sebacic acid, and polybutylene azelaic terephthalate. Other resins may include only one type or two or more types.

[0096] The content of the other resins mentioned above is not particularly limited, but is preferably 50 parts by weight or less, more preferably 40 parts by weight or less, and even more preferably 30 parts by weight or less, relative to 100 parts by weight of all P3HA resins. The lower limit of the content of the other resins mentioned above is not particularly limited and can be 0 parts by weight.

[0097] The above-mentioned resin composition may further include inorganic fillers. By including inorganic fillers in the above-mentioned resin composition, the crystallization rate is increased, which can improve the effects of reducing burrs and improving the production cycle.

[0098] There are no particular limitations on the inorganic fillers mentioned above; examples include talc, calcium carbonate, mica, silica, glass fiber, and glass particles.

[0099] Relative to 100 parts by weight of all P3HA resin, the content of the aforementioned inorganic filler is, for example, 0 to 60 parts by weight, preferably 5 to 50 parts by weight, more preferably 10 to 40 parts by weight, and particularly preferably 15 to 35 parts by weight. When the content of the inorganic filler is within the above range, sufficient crystallization rate and toughness can be achieved.

[0100] Furthermore, without impairing the effects of the present invention, the above-described resin composition may contain additives that can be used with P3HA-type resins. Examples of such additives include: colorants such as pigments and dyes, deodorants such as activated carbon and zeolite, fragrances such as vanillin and dextrin, plasticizers, antioxidants, weather resistance modifiers, ultraviolet absorbers, crystallizing nucleating agents, lubricants, release agents, water repellents, antibacterial agents, and slip modifiers. The additive may contain only one type or two or more. Those skilled in the art can appropriately determine the content of these additives according to their intended use.

[0101] (Injection molding)

[0102] In this manufacturing method, injection molding is preferably performed at a resin composition temperature above the melting point peak end temperature in differential scanning calorimetry (DSC). With this configuration, the resin melts sufficiently, resulting in an excellent appearance. It should be noted that the melting point peak end temperature can be determined using the method described in the examples below.

[0103] This invention is not limited to the above-described embodiments. Various modifications can be made within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of this invention.

[0104] That is, one embodiment of the present invention is described below.

[0105] <1> A method for manufacturing an injection-molded article, which uses a mold apparatus containing a resin composition of a poly(3-hydroxyalkanoate) resin, wherein,

[0106] The aforementioned poly(3-hydroxyalkanoate) resins are copolymers that contain at least one of the following copolymers: copolymers of 3-hydroxybutyrate units and other hydroxyalkanoate units.

[0107] When the mold in the above-mentioned mold device is closed, the maximum width of the parting line that connects to the cavity in the mold is less than 30 μm, and an exhaust part is provided at a different parting line that connects to the cavity in the mold, with the maximum width of the opening of the exhaust part being 1 to 50 μm.

[0108] <2> According to the manufacturing method described in <1>, the mold has two or more cavities of the same shape.

[0109] <3> According to the manufacturing method described in <2>, in the above-mentioned mold device, the distance from the nozzle tip of the injection molding machine to each of the above-mentioned cavities is equal.

[0110] <4> The manufacturing method according to any one of <1> to <3>, wherein the mold has a straight flow channel and a cross flow channel, and the resin composition in the straight flow channel and the cross flow channel is in a molten state.

[0111] <5> The manufacturing method according to any one of <1> to <4>, wherein the mold has an ingate that can be opened and closed.

[0112] <6> According to the manufacturing method described in <4> or <5>, in the above mold, the total volume of the straight runner, the cross runner and the ingate / the total volume of the cavity is 0.5 to 5.0.

[0113] <7> The manufacturing method according to any one of <1> to <6>, wherein the mold has a mechanism for drawing gas from the venting section.

[0114] <8> The manufacturing method according to any one of <1> to <7>, wherein the structure of the opening of the exhaust section is selected from any one or more of the following: slit type, multi-hole type, sleeve type and switching type.

[0115] <9> The manufacturing method according to any one of <1> to <8>, wherein the 3-hydroxybutyrate unit in the above-mentioned poly(3-hydroxyalkanoate) resin is 80.0 to 99.5 mol%.

[0116] <10> The manufacturing method according to any one of <1> to <9>, wherein the above-mentioned resin composition further comprises a second poly(3-hydroxyalkanoate) resin.

[0117] The aforementioned second type of poly(3-hydroxyalkanoate) resin comprises at least one of the following copolymers: copolymers of 3-hydroxybutyrate units and other hydroxyalkanoate units.

[0118] The 3-hydroxybutyrate unit in the above-mentioned second type of poly(3-hydroxyalkanoate) resin is 65.0 to 90.0 mol%.

[0119] <11> The manufacturing method according to any one of <1> to <10>, wherein the injection molding in the manufacturing method of the injection molded article is performed at a resin composition temperature above the melting point peak end temperature in differential scanning calorimetry.

[0120] <12> The manufacturing method according to any one of <1> to <11>, wherein the above-mentioned resin composition further comprises inorganic filler.

[0121] Example

[0122] The present invention will now be described in more detail based on embodiments, but the present invention is not limited to these embodiments.

[0123] 〔Material〕

[0124] In the examples and comparative examples, the materials shown in Table 1 were used. PHA-H was manufactured according to the method described in Example 9 of International Publication No. 2019 / 142845.

[0125]

[0126] [Measurement and Evaluation Methods]

[0127] The measurements and evaluations in the examples and comparative examples were performed according to the following methods.

[0128] (Temperature at the end of the melting point peak)

[0129] The particles obtained by the method described in the (granulation) section (described later) were cut into films with a sample weight of 4.5 ± 0.2 mg. The films were then placed on the bottom of an aluminum disk, and the melting point peak was determined using a differential scanning calorimeter. The temperature at which endothermic reaction was not confirmed was taken as the end temperature of the melting point peak, obtained by heating from 30 °C to 180 °C at a rate of 10 °C / min under a nitrogen flow.

[0130] (Burry thickness)

[0131] The spoons from the 10th, 20th, 30th, 40th, and 50th injections were recovered. Next, the spoons were observed under a microscope at 400x magnification. For the spoon with the largest burrs, the maximum burr thickness was measured using the software accompanying the microscope. A maximum burr thickness of 65 μm or less was considered small, and a maximum burr thickness of 60 μm or less was considered sufficiently small.

[0132] [Examples 1-13, Comparative Examples 1-2]

[0133] The injection molded articles of Examples 1-13 and Comparative Examples 1-2 were manufactured according to the following method.

[0134] (Preparation of PHBH mixture)

[0135] The amount of each raw material Ce (kg) in Examples 1-13 and Comparative Examples 1-2 was determined using the following formula (1) based on the number of each raw material We added to the PHBH mixture and the total number of PHBH mixture Wt added as recorded in Tables 2-4.

[0136] Ce=10×We÷Wt···(1)

[0137] The measured raw materials were fed into a 75L super mixer manufactured by KAWATA MFG and mixed at 300 rpm for 3 minutes to produce a PHBH mixture.

[0138] (granular)

[0139] Using a TEM26SS (L / D = 60) manufactured by Toshiba Machine Co., Ltd., the drum temperature was set to 140°C and the screw speed was set to 100 rpm. Based on the total amount of PHBH mixture added Wt and the amount of inorganic filler added Wf, the feed rate F1 (kg / hr) of the PHBH mixture at the screw root was determined by the following formula (2), and the feed rate F2 (kg / hr) of the side-feed inorganic filler was determined by the following formula (3).

[0140] F1=10×Wt÷(Wt+Wf)···(2)

[0141] F2=10×Wf÷(Wt+Wf)···(3)

[0142] The filament obtained from the die head is passed into a water tank filled with 45°C warm water to solidify it, and then cut into granules using a granulator.

[0143]

[0144]

[0145] [Table 4]

[0146]

[0147] (Fabrication of injection-molded parts)

[0148] A spoon with a total length of 160mm was injection molded using a Si-180V injection molding machine manufactured by Toyo Kikaku Metal Co., Ltd. The structures of the molds used for injection molding in each embodiment and comparative example are shown in Tables 6-8. The change in the total volume of the straight runner, cross runner, and ingate / total cavity volume was implemented by changing the diameters of the straight runner, cross runner, and ingate. Furthermore, in the injection molding machines of Examples 1-3 and 6-13, and Comparative Examples 1-2, the ingate (valve pin) can be opened and closed. Additionally, the hot ingate temperature and manifold temperature of the hot cross runner were set to 170°C in Examples 1-3 and 6-12, and Comparative Examples 1 and 2, and to 160°C in Example 13. In Examples 4 and 5, which used a cold cross runner, a mold without heating mechanisms in the cross runner, ingate, and manifold was used. Figure 2 Three-piece molds with identical structures. Molding conditions are shown in Table 5. Regarding the venting section, the slit method follows... Figure 4 Implementation, sleeve method according to Figure 5 Implementation.

[0149] [Table 5]

[0150]

[0151] 〔result〕

[0152] For the injection-molded articles obtained in Examples 1-13 and Comparative Examples 1-2, the results of measuring the burr thickness are shown in Tables 6-8. It should be noted that "-" in the tables represents "0" or "none".

[0153]

[0154]

[0155] [Table 8]

[0156]

[0157] As shown in Tables 6-7, the maximum burr thickness of Examples 1-13 is small or sufficiently small. Furthermore, compared to other embodiments without a gas suction mechanism, the maximum burr thickness of Examples 8-10, which have a gas suction mechanism, is further reduced.

[0158] On the other hand, in Comparative Example 1, the maximum width of the parting line connecting to the cavity inside the mold is 40 μm, and in this case, the maximum burr thickness is greater than 60 μm. Additionally, in Comparative Example 2, the gap between the parting line and the parting line is 60 μm, and in this case, the maximum burr thickness is also greater than 60 μm.

[0159] Therefore, it can be seen that when using a specific mold (i.e., a mold in which the maximum width of the parting line connected to the cavity in the mold is less than 30 μm when the mold is closed, and an exhaust portion is provided at a different location from the parting line connected to the cavity in the mold), continuous production can be carried out stably without burrs.

[0160] Industrial applicability

[0161] According to the invention of this application, continuous production can be carried out stably without producing burrs. Therefore, it is preferably used in the field of manufacturing injection molded articles using P3HA resins (especially P3HA resins with a high 3HB ratio) and other fields.

Claims

1. A method for manufacturing an injection-molded article, comprising using a mold apparatus for a resin composition containing a poly(3-hydroxyalkanoate) resin, wherein, The poly(3-hydroxyalkanoate) resin is a copolymer that comprises at least one of the following copolymers: a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units. When the mold in the mold device is closed, the maximum width of the parting line connecting with the cavity inside the mold is less than 30 μm, and venting sections are provided at locations different from the parting line connecting with the cavity inside the mold. The maximum width of the opening of the venting section is 1~50 μm. In the mold, the total volume of the straight runner, cross runner, and ingate / the total volume of the cavity is 0.5 to 5.

0.

2. The manufacturing method according to claim 1, wherein, The mold has two or more cavities of the same shape.

3. The manufacturing method according to claim 2, wherein, In the mold assembly, the distance from the nozzle tip of the injection molding machine to each cavity is equal.

4. The manufacturing method according to any one of claims 1 to 3, wherein, The mold has a direct flow channel and a cross flow channel, and the resin composition in the direct flow channel and the cross flow channel is in a molten state.

5. The manufacturing method according to claim 4, wherein, The mold has an ingate that can be opened and closed.

6. The manufacturing method according to any one of claims 1 to 3, wherein, The mold has a mechanism for drawing gas from the venting section.

7. The manufacturing method according to any one of claims 1 to 3, wherein, The structure of the opening of the exhaust section is selected from any one or more of the following: slit type, multi-hole type, sleeve type, and switch type.

8. The manufacturing method according to any one of claims 1 to 3, wherein, The 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin are 80.0~99.5 mol.

9. The manufacturing method according to any one of claims 1 to 3, wherein, The resin composition further comprises a second poly(3-hydroxyalkanoate) resin. The second poly(3-hydroxyalkanoate) resin comprises at least one of the following copolymers: copolymers of 3-hydroxybutyrate units and other hydroxyalkanoate units. The 3-hydroxybutyrate unit in the second poly(3-hydroxyalkanoate) resin is 65.0~90.0 mol.

10. The manufacturing method according to any one of claims 1 to 3, wherein, Injection molding is performed in the method for manufacturing the injection molded article at a resin composition temperature above the melting point peak end temperature in differential scanning calorimetry.

11. The manufacturing method according to any one of claims 1 to 3, wherein, The resin composition further comprises inorganic fillers.

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